The subject of solarplate came up, and as I am participating in a collaborative printmaking project with faculty/students from several colleges with solarplate as a basis, I thought I would add a couple things to the discussion. The group will end up with a collaborative portfolio, some drawing directly on the plates, some combining photographic and drawing processes, some using the film stuff Z'Acryl (that and Imagon I know nothing about), some not doing solarplate at all.
I am testing several methods of negatives for this process. The first two dispense with the double exposure/aquatint screen, and are lower tech ways of teaching solarplate to those not digitally savvy.
One is a simple bitmap--input 600/output 600, black ink only. That works very well for detailed imagery, as it incorporates a dot pattern into the image that ends up not being perceptible in the final image. However, the printer you use to make your negs really determines exposure time. For instance, the Epson 2400 blacks are not very dense, but the Epson 3000 and Epson 2200 are. And, if there are areas of large darks in the image, they will still open bite. Solarplate has two major problems, open bite, and mottledness.
Second, is the Henrik Boegh method of making your image a halftone--you first lower the tonal range of the image with a curve, by pulling down the top right of the diagonal curve line so that input is is 100 output is 80, then under your print with preview screen adding a halftone screen at 65 lpm/45 angle/diamond. This works surprisingly well, but of course you are clipping tones with the way of handling the curve. There, too, was open bite in larger areas of dark, so for a really dark image like, for instance, Flor Garduno (sp?) does, it might not be the best.
Third, the most accurate and professional way of handling solarplates but one that requires more digital savviness: I am biting the bullet and using the aquatint screen exposure/negative exposure--doing the double exposure technique. I know there is a way to create a stochastic aquatint screen in computer if anyone can share it, but I bought the thing--not cheap. So now I am working at calibrating exposure times with the screen and then the negative, and then after I get that proportion figured out (solarplates under UVBL are about 10 minutes total exposure and the aquatint screen can be up to 1/3 or 1/2 that) I will then calibrate a custom curve using the Precision Digital Negatives system and colorized negs. On this one, no open bite.
I will highly recommend two books, the Heinrik Boegh Handbook of NonToxic Intaglio and Welden's Printmaking in the Sun. Both are must-haves. The Keith Howard books are also good, but I find myself referring to Boegh's the most. Second, buying the plates directly from Dan Welden is pretty darn cheap, aside from the fact he is so nice and helpful.
Hope this helps whoever it was many emails ago who asked questions on solarplate!